Imaging techniques are an important tool in medical technology. For example, magnetic resonance (MR) may be used to produce clinical sectional images that have high and variable soft tissue contrasts. One or more MR coil apparatuses may be used, that include one or more magnetic resonance antennas, referred to as coil elements, for transmitting and/or receiving high frequency electromagnetic signals.
Special MR coil apparatuses, for example, local coil arrangements, may be used for MR imaging of peripheral body regions such as joints in arms and legs. It is desirable that such a local coil arrangement may be adjusted optimally to the size and/or shape of the examined parts of the body. A good filling factor, that the adjustment makes achievable, and/or a minimized spatial distance between examination object and coil elements, that the local coil arrangement includes, provides for an improvement in the signal-to-noise ratio and in the image quality. If the local coil arrangement is configured to be too big, the image noise increases. If the local coil arrangement is too small in design the arrangement may impair patient comfort, for instance by exerting an unpleasant pressure, or the arrangement may not be usable at all.
The known local coil arrangements may be classified as rigid types configured to fit the body region and as flexible types. Rigid local coil arrangements that are often used for head examinations for instance, are optimally configured to fit an average patient anatomy, so as to include as many patients as possible (usually 95% percentile). For patients with small or intermediate anatomy dimensions, however, the best possible image quality is not achieved for reception because the coil elements do not lie optimally close to the body of the patient.
Flexible local coil arrangements may compensate for the lack of adjustment often only by accepting bulges and protrusions of portions of the local coil arrangement. For example for cylindrical body shapes such as knees and elbows, the coil elements normally have a different overlap or a different gap that limits the image quality that may be achieved. For example, the unexamined German application DE 10 2011 007 065 A1 describes a knee coil including a rigid part and a flexible part. The unexamined German application DE 10 2006 027 189 A1 discloses a local coil arrangement that may be varied in both height and width. The unexamined German application DE 10 2015 210 529 A1 discloses a local coil arrangement including an adjustable supporting structure including a plurality of support members that form a closed chain.